The present invention relates generally to marine mining and, more particularly, to an apparatus and method for the delivery, loading and retrieval of containers used in raising materials, such as mineral nodules, from the ocean floor.
It has been known for many years that vast amounts of minerals are present in the oceans of the world, particularly in mineral-rich nodules found on the ocean floor. Such nodules contain significant quantities of valuable nickel, copper, cobalt, manganese and other components.
In recent years, attempts have been made to mine or harvest these mineral-rich nodules, however, because the nodules are found at depths which sometimes exceed 12,000 feet below sea-level and because of the severeness of the ocean environment, many difficulties have been encountered which have made the mining technically and economically impractical, and sometimes impossible. The motion of the sea and wind must be contended with, especially during storm situations; equipment must be remotely controlled from a great distance; the nodules, which are distributed over the expansive ocean floor, must be located and collected; and failed equipment located in the ocean or on the ocean floor must be repaired or replaced. One particularly difficult problem encountered is in raising the nodules to the surface for recovery by a surface ship once the nodules have been collected.
One technique which has been tested utilized a continuous-loop bucket dredge strung between a surface ship and a nodule collection vehicle on the ocean floor. The dredge comprised a long loop of cable having scoops spaced along its length. The scoops picked up sediment containing the nodules from the sea-bed, carried their contents to the ship for dumping, and returned to the ocean floor to repeat the process. One disadvantage of this technique is the susceptibility of the cable to breakage, which results in delayed operations and loss of expensive dredge equipment.
Another technique tested utilized a pipe extending between a surface ship and the ocean floor with pumps used to bring the nodules to the surface. One such system is described in U.S. Pat. No. 3,908,290. This type of system requires an extremely long length of piping, and massive air-injection or hydraulic pumps.
One more technique to raise gathered nodules from the ocean floor is described in U.S. Pat. No. 3,314,174. The nodules are loaded in a container and the container is raised to the surface by a hoist located on a surface ship. When the container is emptied, it is returned to the ocean floor for refilling.
Yet another technique is described in U.S. Pat. No. 4,010,560 and involves use of an inflatable bag or balloon to lift a crate filled with nodules to the surface. The weight of the crate carries it to a nodule collection vehicle on the ocean floor, guided by cables extending between a surface ship and the collection vehicle. After being filled to a predetermined level, the crate is released from the cables and ejected from the collection vehicle. The lifting bag attached to the crate is then inflated to carry the crate to the surface.
Such an independent lifting technique overcomes many of the inherent technical problems which are believed to make operation of the previously mentioned techniques at great depths impractical. One disadvantage, however, of using an inflatable lifting bag is that the bags must be inflated while in water as much as 12,000 feet deep. The pressure at such a depth is approximately 7,000 pounds per square inch, and, of course, any source of air or other gaseous substance used to inflate the bag would have to be capable of generating gaseous pressure greater than that of the surrounding environment. Not only would a source of very high pressure have to be used, the flow rate of the source would have to be sufficient to minimize the time delay that occurs after a crate is ejected and before the bag is inflated enough to begin ascent.
Furthermore, the inflatable lifting bag technique requires the bag be provided with a pressure relief valve to keep the differential pressure between the interior of the bag and the surrounding environment within a tolerable limit as it ascends to permit buoyancy, but prevent rupture. The crate must also be equipped with a suitable sonar or other device to facilitate its location and recovery once it reaches the surface. Currents and the travel of the surface ship during the time period required for inflating the bag and the crate's ascent could result in the crate surfacing many miles from the surface ship.
It will therefor be appreciated that there has been a significant need for an apparatus and method for the delivery, loading and retrieval of containers from the ocean floor which is technically and economically feasible. Ideally, such an apparatus and method should include an independent lifting means that does not require inflation while on the ocean floor, and should provide for safe, rapid and controlled ascent of containers once filled with material. The present invention fulfills this need, and further provides other related advantages.